ANSI IEEE Std 946-2004 pdf download IEEE Recommended Practice for the Design of DC Auxiliary Power Systems for Generating Stations
3. Definitions
For the purposes of this recommended practice, the following terms and definitions apply. The Authoritative Dictionary of IEEE Standards [B2], should be referenced for terms not defined in this
3.1 battery capacity: The amp-hours available in an installed battery as measured by test. This is measured, normally after an equalize charge, by a performance or modified performance test. The battery capacity may be larger or smaller than the rated capacity and is expressed as a per cent of rated capacity for a given duration. For lead acid batteries, this is due to degradation of the grid, connections, welds, pellet interface to the grid, crystal surface contact interface of the lead oxides, wet surface interface between the lead oxide and the electrolyte, electrolyte specific gravity, and transport resistance of the hydrogen and oxygen between the positive and negative plates. Since the factors which affect battery performance are varied, the measured battery capacity at a long duration may differ from the measured capacity at a short duration.
3.2 battery rated capacity: The rated amp-hours available in a battery at 100% charge. This is established via“S” or fan curves by a manufacturer’s test of a limited sample of cells using the interconecting hardware supplied with the standard installation. The rated amp-hours may differ as a function of the discharge duration, long duration discharges typically utilizes the available material more effectively. NOTE- See IEEE Std 485 for an example of the manufacturer ‘s sizing curves.
3.3 battery state of charge: A factor between 0 and 100. It establishes the available amp-hours by multiplying the state of charge times the battery capacity times the battery rated capacity for a specified discharge duration. The battery state of charge reflects the conversion or restoration of lead sulfate to lead oxide after a discharge.
4. General
4.1 Description and operation All power generating stations require de auxiliary power systems to operate those de components that must be available should a loss of ac power occur. Some examples of such components are auxiliary motors, cireuit breakers, relays, solenoids, and inverters. The dc source(s) may be one common battery for both power and control or two separate batteries; one for power and another for control and instrumentation. Separate batteries are recommended for special services such as for engine (cranking) starting.